This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-087036, filed Mar. 26, 2001; and No. 2001-087037, filed Mar. 26, 2001, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a thermoelectric module and a heat exchanger equipped with the thermoelectric module.
2. Description of the Related Art
Depletion of resources is expected in the twenty-first century so as to make it very important nowadays to develop measures for effectively utilizing energy, and various systems are being proposed along this line. Particularly, the thermoelectric element is expected to provide a means for recovering the energy discarded uselessly in the past as waste heat. The thermoelectric element has already been put practical use as a module comprising a p-type semiconductor element and an n-type semiconductor element, which are connected in series.
Extensive researches are being conducted on many thermoelectric semiconductor materials in an attempt to achieve a high thermoelectric efficiency. Particularly, strenuous efforts are being made in an attempt to improve the power generation efficiency.
However, the thermoelectric material that has been put into practical use is the Bi (bismuth)-Te (tellurium) system including a Bixe2x80x94Te alloy containing a third element such as antimony (Sb) or selenium (Se). The other materials, which have certainly been used in special fields, have not yet been produced on a commercial basis.
The waste-heat boiler is designed to obtain only steam or warm water through a heat exchanger, and the power required for operating the boiler is introduced from the outside. In recent years, it has been attempted to incorporate a thermoelectric module in the waste-heat boiler so as to produce electric power from the waste heat. In this case, it is desirable for the thermoelectric element to be operated under temperatures as high as possible because the thermoelectric element is capable of utilizing a heat source having a higher temperature. Particularly, it is desirable for the thermoelectric element to be operated under temperatures not lower than 300xc2x0 C.
However, the Bixe2x80x94Te series thermoelectric element is operable under temperatures of at most 200xc2x0 C., failing to satisfy the requirement pointed out above.
An object of the present invention is to provide a thermoelectric module with improved thermoelectric performance under temperatures not lower than about 300xc2x0 C., and to provide a heat exchanger using the particular thermoelectric module.
A first thermoelectric module of the present invention comprises:
a plurality of p-type thermoelectric elements each comprising a p-type semiconductor having a skutterdite crystal structure, each of the p-type thermoelectric elements having a first surface having a high temperature and a second surface having a temperature lower than that of the first surface;
a plurality of n-type thermoelectric elements each comprising a n-type semiconductor having a skutterdite crystal structure, each of the n-type thermoelectric elements having a first surface having a high temperature and a second surface having a temperature lower than that of the first surface, and the p-type thermoelectric elements and the n-type thermoelectric elements being arranged alternately;
at least one first electrode and at least one second electrode connecting the p-type thermoelectric elements and the n-type thermoelectric elements in series;
at least one first alloy layer for bonding the at least one first electrode to the first surface of the one p-type thermoelectric element and to the first surface of the one n-type thermoelectric element adjacent to the one p-type thermoelectric element; and
at least one second alloy layer for bonding the at least one second electrode to the second surface of the one p-type thermoelectric element and to the second surface of the one n-type thermoelectric element adjacent to the one p-type thermoelectric element,
wherein the at least one first alloy layer and the at least one second alloy layer contain Sb and at least one transition metal element selected from the group consisting of Ag, Au and Cu.
A second thermoelectric module of the present invention comprises:
a plurality of p-type thermoelectric elements each comprising a p-type semiconductor having a skutterdite crystal structure, each of the p-type thermoelectric elements having a first surface having a high temperature and a second surface having a temperature lower than that of the first surface;
a plurality of n-type thermoelectric elements each comprising a n-type semiconductor having a skutterdite crystal structure, each of the n-type thermoelectric elements having a first surface having a high temperature and a second surface having a temperature lower than that of the first surface, and the p-type thermoelectric elements and the n-type thermoelectric elements being arranged alternately;
at least one first electrode and at least one second electrode connecting the p-type thermoelectric elements and the n-type thermoelectric elements in series, and the at least one first electrode and the at least one second electrode containing Fe and having a thermal expansion coefficient falling within a range of between 8xc3x9710xe2x88x926/xc2x0 C. and 16xc3x9710xe2x88x926/xc2x0 C.;
at least one first alloy layer for bonding the at least one first electrode to the first surface of the one p-type thermoelectric element and to the first surface of the one n-type thermoelectric element adjacent to the one p-type thermoelectric element; and
at least one second alloy layer for bonding the at least one second electrode to the second surface of the one p-type thermoelectric element and to the second surface of the one n-type thermoelectric element adjacent to the one p-type thermoelectric element,
wherein the at least one first alloy layer and the at least one second alloy layer contain Sb and at least one transition metal element selected from the group consisting of Ag, Au and Cu.
A third thermoelectric module of the present invention comprises:
a plurality of p-type thermoelectric elements each comprising a p-type semiconductor having a skutterdite crystal structure, each of the p-type thermoelectric elements having a first surface having a high temperature and a second surface having a temperature lower than that of the first surface;
a plurality of n-type thermoelectric elements each comprising a n-type semiconductor having a skutterdite crystal structure, each of the n-type thermoelectric elements having a first surface having a high temperature and a second surface having a temperature lower than that of the first surface, and the p-type thermoelectric elements and the n-type thermoelectric elements being arranged alternately;
at least one first electrode and at least one second electrode connecting the p-type thermoelectric elements and the n-type thermoelectric elements in series, and the at least one first electrode and the at least one second electrode containing silver as a main component;
at least one first silver-antimony alloy layer for bonding the at least one first electrode to the first surface of the one p-type thermoelectric element and to the first surface of the one n-type thermoelectric element adjacent to the one p-type thermoelectric element; and
at least one second silver-antimony alloy layer for bonding the at least one second electrode to the second surface of the one p-type thermoelectric element and to the second surface of the one n-type thermoelectric element adjacent to the one p-type thermoelectric element.
A first heat exchanger of the present invention comprises at least one thermoelectric module selected from the first to third thermoelectric modules of the present invention defined as above.
Further, a second heat exchanger of the present invention performs a heat exchange between a high temperature fluid and a low temperature fluid and comprises a thermoelectric module arranged between the fluid passageway of the high temperature fluid and the fluid passageway of the low temperature fluid, the thermoelectric module comprising:
a plurality of p-type thermoelectric elements each comprising a p-type semiconductor having a skutterdite crystal structure, each of the p-type thermoelectric elements having a first surface and a second surface;
a plurality of n-type thermoelectric elements each comprising a n-type semiconductor having a skutterdite crystal structure, each of the n-type thermoelectric elements having a first surface and a second surface, and the p-type thermoelectric elements and the n-type thermoelectric elements being arranged alternately;
at least one first electrode and at least one second electrode connecting the p-type thermoelectric elements and the n-type thermoelectric elements in series, the at least one first electrode heated by the fluid passageway of the high temperature fluid, and the at least one second electrode cooled by the fluid passageway of the low temperature fluid;
at least one first alloy layer for bonding the at least one first electrode to the first surface of the one p-type thermoelectric element and to the first surface of the one n-type thermoelectric element adjacent to the one p-type thermoelectric element; and
at least one second alloy layer for bonding the at least one second electrode to the second surface of the one p-type thermoelectric element and to the second surface of the one n-type thermoelectric element adjacent to the one p-type thermoelectric element,
wherein the at least one first alloy layer and the at least one second alloy layer contain Sb and at least one transition metal element selected from the group consisting of Ag, Au and Cu.